Historically, a modal analysis system consisted of a two-channel measurement instrument, together with a source of excitation such as a sine wave, a hammer strike or random noise generator. Measuring a structure for its modal characteristics under these conditions is fairly straightforward, but is also tedious due to the necessity of placing accelerometers at several different points on the object to be measured, and repeating the measurement. As the measurements became more complex, and as new modal analysis algorithms placed constraints on how measurements could be made, the need for more data collection and more measurement channels arose.
Although in principle it would be possible to simply add more measuring instruments to increase the data capacity, a practical limit of cost and complexity is soon reached. As a result, there is a need for a measuring instrument that is capable of efficiently processing a number of input channels.